DC and his group performed pioneering research on the cleavage fracture micro-mechanisms and prediction of the ductile-brittle transition in high-strength ferritic grades of steels, considering the role of particles, microstructural parameters and crystallographic texture. The research work has made a significant scientific contribution to substantiate the fundamental concepts on the definition of 'effective grain size' and the delamination phenomenon in high strength steels used for the structural, reactor, and naval applications.

DC and his group also contributed ground-breaking research on the development, characterization, and effects of ultrafine and bimodal grain structures in steels by innovative thermomechanical processing routes (simulated in Gleeble® system).

Besides fundamental research, exemplary application-oriented research studies have been performed in different areas of National importance as listed below through the projects funded by DST-SERB, CSIR, Naval Research Board, BRNS-DAE, Steel Authority of India (SAIL), and Tata Steel.

• The research projects supporting DMRL-DRDO, Hyderabad, on the development and characterization of high-strength steels (YS > 1000 MPa) with high impact toughness at sub-zero temperature (> 78 J at -40°C), for maritime and also armour applications, can be regarded as a significant National contribution. One of the project outcomes has been published in Naval Research Board Magazine Vol. III, 2019.

• Recently developed a new grade of boron added modified 9Cr-Mo steel, with optimum B (80-90 ppm) and N concentrations (100-110 ppm), achieving much superior creep resistance than the existing grades of steels, as one of the most advanced high-temperature materials for fossil-fuel power plants (In a collaborative project with IGCAR, Kalpakkam). Besides, an in-depth study improved the combination of impact toughness along with creep resistance for a boron-free modified 9Cr-1Mo steel (in starting condition) to prevent accidents and hazard in Nuclear Power applications.

• Noteworthy research performed on the high-strain-rate tensile properties of steels (up to 800/s) for crash-resistance automotive applications is possibly the first of this kind in India (with CSIR-NML). Highly recognized research on creep and low-cycle fatigue behaviour (both at elevated temperatures) of the welded 9Cr-1Mo steel has been conferred with Dr. Nijhawan Award as the best technical paper published in 2014-15 from CSIR-NML.

• Recently executed a very successful project of National importance on the characterization of Cold Rolled Grain Oriented (CRGO) Silicon steel to support RDCIS-SAIL (the funding agency) and MIDHANI to develop CRGO steel in India, for electrical applications.

• Successfully completed two National Mission projects by setting-up necessary testing facilities at IIT Kharagpur and performing the required FCGR and fracture testing on the development of materials for the Advanced Ultra-Supercritical (AUSC) Power Plant technology, coordinated by the Mission Directorate involving BHEL, NTPC and IGCAR.

• Identified the segregation and processing related problems responsible for T-72/T-90 tank barrel material failure, to support the Metal & Steel Factory, Ishapur, funded by the Ordnance Factory Board.

Basic research contribution

1) Microstructure-property relationship in steels with emphasis on impact toughness and ductile-brittle transition phenomenon

Pioneering research on the cleavage fracture micro-mechanisms and prediction of the ductile-brittle transition in high-strength ferritic grades of steels, considering the role of particles, microstructure and texture. The research work has made a significant scientific contribution to substantiate the fundamental concepts on the definition of 'effective grain size' involved in cleavage crack propagation and the delamination phenomenon in high strength steels.

2) Fundamental research on the Ultrafine- and Bimodal Grain Structures: Evolution and Effect

Ground-breaking research on the evolution and characterization of ultrafine and bimodal grain structures in metallic systems through innovative thermomechanical processing (based on Gleeble® simulation). Explained the development of ultrafine- and bimodal grain structures during different stages of thermomechanical processing starting from the role of segregation and heterogeneous precipitate distribution during casting, soaking treatment, thermomechanical processing, and annealing treatment. Subsequently, evaluated the effect of ultrafine- and bimodal grain structures on the mechanical properties.

Applied Research contributions on various fields of steel metallurgy of national importance

1) Applied research on the modified 9Cr-1Mo steel

Modified 9Cr-1Mo steel is one of the major structural materials chosen for both fossil-fuel power plants and Prototype Fast Breeder Reactor (PFBR) for steam generator application. Continuous development of modified 9Cr-1Mo steel clad tube and 9Cr-1Mo steel wrapper for future metallic fuel reactors are in progress. Type-IV cracking of the welds is a serious problem associated with the modified 9Cr-1Mo regarding steam generator application under severe creep thermal exposure. Controlled addition of B is beneficial for improving Type-IV cracking resistance; however, the N content is also important from that respect. Under the BRNS funded project entitled 'ALLOY SEGREGATION IN BORON ADDED 9CR-1MO STEEL UNDER DIFFERENT THERMAL AND THERMO-MECHANICAL CONDITION', ended in 2020 in collaboration with IGCAR Kalpakkam, a new grade of Boron added steel has been developed (containing 70 ppm B, 110 ppm N). The newly developed grade shows a far superior creep resistance than the existing grade of Boron free and Boron added steels developed under the atomic energy commission for high-temperature applications in power plants.

Besides, an in-depth study performed under the BRNS funded project ‘Process induced Microstructural variation towards improved ductile-brittle transition temperature of 9Cr-Mo steel’, completed in 2015, identified the optimum processing condition (1025-1100 °C normalizing, 750 °C tempering) for achieving the best combination of impact toughness and creep resistance in modified 9Cr-1Mo steel to prevent accidents and hazard in Nuclear Power applications under the exposure of creep and irradiation.

2) Applied research on naval grade steels with high strength and toughness

Over the past few decades, Indian Navy has been driving the research on the indigenization of the naval steels, involving different laboratories of DRDO such as DMRL, NMRL and DMSEDE along with the Industrial partners like SAIL. Upon the success of the previous grades (DMR249A and 249B), Indian Navy and DRDO engaged themselves in the development of 780 MPa yield strength steel to meet the futuristic needs of the Indian Navy. DC’s group has been involved as a consultant to DMRL for the successful completion of this project. Subsequently, under an NRB funded research project entitled ‘Improving the impact transition behaviour of high strength naval steels by refining the effective grain size of matrix microstructure’ (Project No. NRB-350/MAT/14-15) extensive information and test results have been generated on the effects of processing parameters on the microstructure-strength-impact toughness combination in the newly developed 780 MPa grade naval steel. Based on such results, the steel can be processed in various ways to meet different property requirements, or used for varied applications in naval vessels. At present, a superior grade of naval steel is being developed through another collaborative research to achieve a minimum yield strength of 1000 MPa, along with a minimum 78 J impact toughness at -40°C. Through various trials performed at IIT Kharagpur, the optimum composition for achieving the target properties has been identified.

3) Applied Research services for identifying the metallurgical problems responsible for the failure of T-72/T-90 tank barrels

The report published in Business Standard (June 13, 2013) and several other news-media on the topic of ‘Ammunition bursts in T-72 tanks barrels cause concern for Army’ indicates a problem of high national importance. The metallurgical properties of the tank barrel material and the problems associated with barrel failures have been investigated by DC’s group in the project entitled ‘Research services for studying and analysing the phenomenon of segregation in T-72/T-90 tank barrels’, to support the Metal & Steel Factory, Ishapur, under the Ordnance Factory Board. The project report is submitted recently with an important finding showing the presence of segregation of alloying elements in Tank Barrel steel. The importance of ensuring sufficiently rapid cooling during the quenching treatment to avoid the formation of undesired bainite constituent has also been demonstrated. For the first time, such a detailed investigation on the metallurgical quality of tank-barrel material has been conducted.

Besides the examination of tank barrel material, DC’s group also investigated the problem of Cartridge Case-failure, and provided metallurgical solutions for a new ‘Artillery Shell Design’ for the Ordnance Factory, Ambajhari, as a part of a collaborative IMPRINT project (led by Prof. P. K. Ray at IIT Kharagpur). Presented to the Ordnance Factory Board, chaired by Mr. Saurabh Kumar, the concepts involved in the fragmentation behaviour and lethality of the artillery shells.

4) Development of high-strength bainitic steels for Indian Railways

The bainitic steel is the preferred material for rails and wheels in UK and Europe, due to its higher strength, toughness and superior wear resistance, as compared to the pearlitic rail steels used in India. Considering the importance of railway safety and to accommodate the high-speed trains, significant development of rail steel is essential in India. Supporting the departmental colleague, Prof. S.B. Singh (project PI), DC (Co. PI) investigated a project, in collaboration with the Railway Research Board, on the development of bainitic rail steel for the Indian Railways. The steel developed achieved superior properties as compared to the existing grades of rail steels manufactured in India. Significant fundamental understanding has also been generated through this research on the bainitic transformation in steels, as well as establishing the microstructure-property correlation in bainitic steels.

The major contributions of the DC’s group to the collaborative research with the steel industries in India

India being the 2^nd largest steel producer, and 3^rd largest finished steel consumer in the world, the Government of India approved the National Steel Policy (NSP) in May 2017 to present the government's long-term vision and thrust towards the Indian domestic steel sector. National Steel Policy 2017 envisages 300 MT steel-making capacity and 160 kgs per capita steel consumption by 2030-2031. India’s finished steel consumption is anticipated to increase from 81.5 MT in 2015-16 to 230 MT by FY2030-31. The Construction and Infrastructure is the largest sector of steel consumption in India and the requirement in this sector is expected to increase almost 3 times, i.e., from 50.5 MT in 2015-16 to 133 MT by 2030-2031. The structural steels used in the construction of buildings, bridges, highways, airports and ports, power projects including pipeline transmission of oil and gas, water transportation come under this category. DC’s group has provided a significant research output in the areas of compositional design, processing, microstructural and mechanical characterization of various grades of structural steels, primarily ‘microalloyed’ high-strength low-alloy (HSLA) steels, in collaboration with the Indian Steel Industries such as, RDCIS-SAIL and Tata Steel.

News regarding the failure of cars manufactured in India in Global crash test emphasizes the need for application-oriented material development (Reference: BBC News: ‘Popular Indian cars fail crash tests conducted by a UK-based car safety watchdog’ Nov 4, 2014). Noteworthy research performed by DC’s group in collaboration with CSIR-NML on the assessment of high-strain-rate (up to 800/s) tensile properties and deformation behaviour of automotive-grade steels (manufactured by Tata Steel) for crash-resistance automotive applications sets the benchmark for the upgradation of the existing automotive steels produced in India, to meet the stringent international safety standard.

There has been a substantial effect by DC’s group to solve the serious problems encountered during the processing of advanced grades of ferritic stainless steels (ridging defect) and duplex stainless steels (hot-cracking problem) in collaboration with Jindal Stainless Limited, Hisar. Besides, tremendous effort has been put forward to develop and characterize the special grades of steels in India (like CRGO steel), having a high national requirement.

1) The project entitled 'Understanding precipitation behaviour and micro-structural evolution at different stages of processing of CRGO steel

Significant contribution has been made by the DC’s group in the characterization of cold-rolled grain-oriented steel (CRGO), where the steel was developed under a collaboration between SAIL and MIDHANI. The project has identified the best combination of ferrite grain size (average grain size as large as 11.5 mm) and texture conditions (62% grains following ideal Goss {110}<001> orientations) out of various pilot-scale trials. The developed steel achieved a satisfactory level of magnetic flux density of 1.5 Tesla. The CRGO steel is a special Fe-Si alloy that is used in the electrical applications as transformer core laminates and has to be imported. This steel is presently under development at SAIL and MIDHANI.

2) Development of high strength structural steels through precipitation-recrystallization interaction and precipitation strengthening

The honourable Prime Minister of India, Shri Narendra Modi during his Independence Day speech (in 2019) announced the National Infrastructure Pipeline (NIP), which is a group of social and economic infrastructure projects over 2020-2025. ₹102 lakh crore (US$1.4 trillion) is sanctioned by Finance Minister in 2019-2020 budget and an additional ₹111 lakh crore will be required for this programme. NIP is a pillar of GoI’s aim to become a $5 trillion economy by 2025.

At present the high-strength structural steel grades are produced as per Indian Standard IS:2062, which does not specify Charpy Impact Value at either 0 °C or -20 °C for E410 (YS > 410 MPa) grade upward. This imposes restrictions on its usage in the sub-zero application, like in high altitude cold terrain. Therefore, the development of high strength structural steel grades with adequate sub-zero toughness would help in promoting their application in colder regions. The structures made with high strength steel will be lighter which will help in their transportation, in general, and to high altitude terrains in particular where civil construction is preferably steel structures.

For the development of high-strength structural steels with high impact toughness, a significant research emphasis has been paid by DC’s research group on the aspects like (i) precipitation-recrystallization interaction during thermo-mechanical processing for achieving substantial grain refinement and (ii) the identification of optimum soaking temperature, cooling-rate and coiling-temperature for achieving the maximum precipitation strengthening (as high as 300 MPa) in natural air-cooled Nb- and V-microalloyed steels and also on a recently developed Ti-Mo grade steel (manuscript under review). The steels developed are in use for flat-product and long-product applications in support of RDCIS-SAIL and Tata Steel Jamshedpur. The concerned research group has been undoubtedly one of the most prolific and efficient users of Gleeble® system (in collaboration with RDCIS-SAIL) for thermomechanical processing simulation of industrial grades of steels.

There has also been noteworthy effort on the assessment of bendability and anisotropy in steel plates during bending of high-strength structural steels and linepipe steels (during pipe-making processes), in collaboration with Tata Steel Europe and Tata Steel India. India has a huge opportunity to cater to the vast demand of quality API (American Petroleum Institute) grade steels to the domestic as well as, to the International market in near future.

3) Research problems on stainless steels

DC’s group has performed significant research in collaboration with Dr. L.K. Singhal from the Jindal Stainless Limited, Hisar plant, on the duplex- and the ferritic stainless steels to identify the root-causes behind the hot-cracking in duplex stainless steel (a novel finding on the detrimental effect of dynamic strain-induced transformation) and the ridging-defect in ferritic stainless steel, and suggested remedial measures for avoiding such defects.

4) New specimen design for impact testing of TMT rebar

Ensuring the quality of thermo-mechanically treated reinforcement steel bars (known as TMT rebars) has been a concern as per the news report entitled ‘More than two-thirds of TMT bar brands manufactured in India fail quality tests’ (Business Today, October 24, 2018). Due to the round cross-section, varying sizes, and the microstructural variation along the diameter, it is extremely difficult to prepare suitable specimen for performing the Charpy impact testing of the TMT rebars. In collaboration with Tata Steel Jamshedpur, a project led by DC proposed a new ‘non-standard’ specimen design for the impact toughness testing of construction rebars. Also investigated the effect of thermal exposure (in fire like situation) on the impact toughness of TMT rebar. Such efforts contribute to the structural safety and reliability during impact loading, either under freezing environmental conditions or under fire, having a tremendous potential of saving human life and property. A joint patent application has been filed by Tata Steel and IIT Kharagpur.

5) Detecting and solving the problem of defected silver medallions

Identified the root-cause (casting defects) behind the failure in sterling silver medallions manufactured by India Government MINT at Alipur Kolkata and showed alternate casting practices to solve the problem.

Collaborative studies that are performed with the Institutes abroad

1) The study on the Bendability of high-strength steel in collaboration with Prof. Claire L Davis, Warwick Manufacturing Group, the University of Warwick UK and Tata Steel Europe

Through a Joint Ph.D. student as a part of the collaborative programme between IIT KGP and the University of Warwick in UK, DC’s group has been involved in collaborative research with Prof. Claire L. Davis at the Warwick Manufacturing Group (WMG) on ‘the bendability of advanced high-strength strip steels’ manufactured by Tata Steel Europe. Very limited studies are available on the bending performance of advanced high strength steels and the failure associated with bending. Cold-bending is, however, an essential requirement for high-strength steels used in structural applications. A collaborative study imparted significant contribution to understanding the effect of complex (bainite + martensite) microstructure of advanced high strength (YS > 700 MPa) steels on the failure mechanisms during bending.

2) Approval of the Project funded by Vanitec® UK

A project entitled “Development of High‐Strength Vanadium Microalloyed Steels for Structural Purposes”, having DC as the principal investigator has been sanctioned recently for funding (worth (USD 165607, i.e., INR 1.22 crore approx) by Vanitec®, a global organization of Vanadium producers having HQ in the UK. A project number V.160 is assigned to the project. The project will start at IIT Kharagpur in February 2021 for 3 years duration, in collaboration with Dr. Vinod Kumar, Chief General Manager, RDCIS-SAIL in Ranchi, on the development of Vanadium containing special grades of steels. The project is to be coordinated by David N Crowther, Technical Consultant, Vanitec Ltd. (david.crowther@vanitec.org) and approved by Mr. John Hilbert, the CEO of Vanite. (Website: http://vanitec.org/)